Thanks do you normally have the liner brown when you’re done or do you finish it with something else, the sights will be flush
Most flash hole liners these days are stainless steel, which won't brown. I install the liner with a good coat of automotive anti-seize compound, then wipe off excess thoroughly. Plug the hole in the liner with a bit of beeswax or modeling clay to keep chemicals out of bore. Degrease the whole area well. Similar technique for percussion gun.
Plug the muzzle with a wooden plug. I take a piece of pine about 1 x 1 x 6 inches and rasp a 3 - 4 inch taper on it, and drive into muzzle. Others will say use hardwood, but pine has worked for me.
Lessons learned the hard way the first time I browned:
High humidity and warmth are necessary. Had access to a browning box heated by a light bulb, now use a tube made of 4 inch white plastic pipe with a damp rag in the bottom and a lamp shining on the outside. Tube is vertical, barrel, rib, etc. hang from top using stove wire.
Follow the directions on the Laurel Mtn. Forge carefully as regards carding and neutralizing the chemicals.
Apply a protective finish of oil, paste wax or beeswax. My best results so far have come from warming barrel with a hair dryer and rubbing in beeswax. Use a toothbrush to get protective finish into nooks and crannies like dovetails and threads.